Hideharu Horikoshi

Effects of heat treatment on absorption bands in OH-free and OH-containing fused quartz

Effects of heat treatment on absorption bands in fused quartz produced by melting natural quartz powder containing 2×1017 cm−3 (sample I) and 1.3×1019 cm−3 of OH (sample II) were studied. Both samples have an absorption peak at ≈5.2 eV. Fluorescent spectra and the results of Gaussian peak decomposition suggest that this absorption is associated with the B2β band with a peak at 5.15 eV and full width at half maximum of 0.42 eV. The 5.15 eV band and an absorption component at 7.5 eV in sample II were annealed out at 1423 K, whereas almost no change was observed in the absorption spectra of sample I. The decrement of the 5.15 and 7.5 eV bands was proportional to the decrement of the OH content. The annealing mechanism in sample II can be explained using a previously proposed model for OH-containing fused quartz wherein the B2β band is the twofold-oxygen-coordinated silicon (=Si:) coordinated with two ≡Si-OH structures. Sample I must have a =Si: structure, but it may not be annealed out because it does not ha...

Influence of OH-group concentration on optical properties of silica glass in terahertz frequency region

We evaluated the optical properties of various types of silica glass with different OH-group concentrations by using terahertz (THz) time-domain spectroscopy. The results show that the absorption coefficient in the THz frequency region varied with the OH-group concentration and that the variation depended only on the OH-group concentration, irrespective of the glass-manufacturing process. On the other hand, the refractive index did not depend on the OH-group concentration. Thus, the THz optical properties of silica glass can be predicted based on the OH-group concentration in the glass, and vice versa.

KrF- and ArF-excimer-laser-induced absorption in silica glasses produced by melting synthetic silica powder

KrF- and ArF-excimer-laser-induced absorption of silica glasses produced by electric melting and flame fusion of synthetic silica powder were investigated. The growth of KrF-laser-induced absorption was more gradual than that of ArF-laser-induced absorption. Induced absorption spectra exhibited a peak at about 5.8 eV, of which the position and width differed slightly among samples and laser species. Widths of ArF-laser-induced absorption spectra were wider than those of KrF-laser-induced spectra. KrF-laser-induced absorption is reproducible by two Gaussian absorption bands peaking at 5.80 eV with full width at half maximum (FWHM) of 0.62 eV and at 6.50 eV with FWHM of 0.74 eV. For reproduction of ArF-laser-induced absorption, Gaussian bands at 5.41 eV with FWHM of 0.62 eV was necessary in addition to components used for reproducing KrF-laser-induced absorption. Based on the discussion of the change of defect structures evaluated from change of absorption components, we proposed that the precursor of the 5...

Temperature and hydroxyl concentration dependences of diffusion coefficients of hydroxyl groups in vitreous silica at temperatures of 850–1200 °C

The hydroxyl concentration and temperature dependences of the diffusion coefficients of hydroxyl groups in vitreous silica were investigated by analyzing the change in the hydroxyl concentration distribution caused by heat treatment around the binding interface between silica glass plates with different hydroxyl concentrations. We confirmed experimentally that the diffusion coefficient is proportional to the hydroxyl concentration, which had been predicted theoretically, and obtained the empirical formula D(c OH) = [(4.9 ± 1.0) × 10−14 m2/swt ppm] × exp[−(8.1 ± 0.3) × 103 K/T] c OH with the hydroxyl concentration c OH and the absolute temperature T, which is valid at least in the temperature range of 850–1200 °C. Using the values calculated using this formula, we can reproduce the hydroxyl concentration profile after diffusion from a silica glass surface induced by heating in a water vapor atmosphere in the literature, which supports the validity of the empirical formula obtained in this study. The relationship between the effective diffusion coefficient in the literature and our result is discussed.